The present invention relates to devices and methods for inspecting soldered connections, more particularly the device of the present invention allows for visually inspecting concealed soldered connections such as those utilized to attach an integrated circuit to a printed circuit board.
With the advances in technology related to integrated circuits (ICs) and in particular to surface mount IC""s and more particular to ball grid arrays (BGAs) and chip scale packages (CSPS) and flip chips (FCs) in addition to the density of ICs utilized in electronics devices it has become increasingly difficult to visually inspect the integrity of the soldered connection between the chip leads and the solder pads on a printed circuit board. In addition, the number of soldered connections per chip has increased while inversely the size of the chip has decreased. While some surface mounted ICs have soldered connections which can be visually inspected because the chip leads project from the edge of the IC, the above-referenced chips cannot be visually inspected without an inspection device because the chip leads project perpendicular to the surface of the IC, and therefore the soldered connections are hidden by the IC.
One method to test the integrity of a soldered connection is that shown in U.S. Pat. No. 6,288,346 Hirofumi et al. wherein a plurality of test lands are disposed upon the circuit board which are connected to solder pads to which a BGA package is to be soldered to in which the continuity between the pins on the BGA can be confirmed. While this inspection method may disclose an open connection it cannot distinguish if there is a xe2x80x98bridged-connectionxe2x80x99 that is where a ball of solder connects more than one pin. A bridged connection may lead to component failure when power is applied to the IC, therefore it is desirable to determine if bridged connections exist. Additionally, the testing method of Hirofumi et al. does not disclose the quality of the soldered connections, that is whether the solder was not heated to a high enough temperature. Therefore, the expected lifetime of the soldered connection cannot be estimated which may lead to more product failure after sales.
Another method to check soldered connections for the above-referenced IC""s is through the use of x-rays. With x-ray inspection, it can be determined whether there are open connections, bridged connections and if the BGA was properly aligned with the solder pads of the printed circuit board. It is not possible to determine the quality of the soldered joint, as described above. In addition, it cannot be determined if excess flux residue remains within the soldered connections. Still further, the use of x-ray inspection requires dedicated equipment in addition to requiring protection from radiation exposure from the x-ray testing device. Lastly, x-ray inspection units require a skilled operator to utilize the device, thereby leading to complexity as well as costs to the overall product.
Still yet another method of inspection that is known is the production of a micrograph in cross-section through a soldered connection. This requires destructive testing, wherein a circuit board is taken from the assembly line and a cut is made passing through the IC to visually inspect the soldered connection. Though, this method will only produce an estimate of the actual soldered connections and requires that conclusions must be drawn as to the operating parameters of the soldering process.
Another known process of inspecting soldered connections is through the use of devices which can transmit images from one location to another, such devices include endoscopes and borescopes. These devices generally have a cylindrical profile and include a plurality of lenses disposed therein for the transmission of an image therethrough. A shortcoming of these devices is that at one end of the device there is disposed a light source adjacent to an image collection device. The light source is utilized to illuminate the area adjacent to the image collection device wherein an image is then reflected into the endoscope and transmitted to the opposite end. The clarity of the transmitted image may be diluted due to excess light emitted and/or reflected from the light source which is transmitted through the device.
Referring now to U.S. Patent Application Publication No. 2001/0024273 Cannon, there is disclosed yet another device for the inspection of soldered connections. In particular, the inspection device shown and described in the above-referenced patent application can be utilized to visually inspect soldered connections of BGA, CSPS, and FCs. The device includes an ocular unit, a lens head, and image transmission unit for transmitting the image receive by the lens head to the ocular unit and an illuminating device. As shown and described in Cannon the device therein may be utilized by placing the lens head adjacent to a BGA to be inspected. An illumination source illuminates the soldered connections while a second illumination source is utilized to backlight the soldered connections. A prism assembly disposed within the lens head receives a reflected image of the soldered connections, the reflected image is transmitted through an image transmission unit and into a camera. An aperture is disposed between the transmission unit and the camera to control the image received by the camera. A shortcoming of the device of Cannon is that the image reflected through the image transmission unit contains xe2x80x9cinterferencexe2x80x9d which leads to the degradation of the image. The term xe2x80x9cinterferencexe2x80x9d refers to the excess reflected light which will be transmitted through the image transmission unit. This excess light will combine with the image to be view, wherein the final combination of the image to be viewed and the interference will then be filtered by the aperture disposed adjacent the camera. An additional shortcoming of the device of Cannon is that the field of view of the lens head is to narrow to visually inspect both the upper solder connections as well as the lower solder connections, in order to visually inspect both, the lens head must be moved away from the soldered connections to provided a greater field of view, though at the cost of clarity of the image. A further shortcoming of the Cannon device is that a prism is utilized to reflect the image of the soldered connections, it is well known that prisms tend to be brittle and therefore require protection. For example, as shown in Cannon the prism is protected by webs, these webs extend beyond the edge of the prism, therefore the leading edge of the prism cannot be lowered such that the prism contacts the circuit board because of the protection webs. Lastly, prisms are very expensive therefore increasing the overall cost of the inspection device, as well as requiring specially trained technicians for repairs and/or servicing of the prism assembly.
Therefore there is a need for a device and methods of use which will enable the visual inspection of soldered connections, wherein the device provides a clear image of both the upper and lower connection without having to readjust the focal length of the device. Additionally, there is a need for an optical inspection device that eliminates interference within the transmitted image, thereby providing a better image of the soldered connection.
In accordance with the present invention there is provided a device for inspecting solder connections between a component and a substrate or between two components or substrates, the device includes an image receiving unit, an image transmitting device, including a first end and a second end, the first end coupled to the image receiving unit. A tip assembly removably coupled to the second end of the image transmitting device, the tip assembly further including a reflective device and an image receiving aperture, the tip assembly configured to transmit an image of the solder connections received by the reflective device, through the image transmitting device, to the image receiving unit, and an illumination device, including a light source, at least one light transmitting device, and at least one light emitting aperture disposed adjacent the image receiving aperture, the light emitting aperture directed towards the solder connections to be inspected.
In accordance with the present invention there is provided a device for optically inspecting soldered connections, the device including, a camera, and an image transmitting device. The image transmitting device including a generally circular cross-sectional profile first end and a second end and a bore extending therethrough, the first end coupled to the camera, and a at least one image transmitting lens disposed within the bore. A tip assembly removably coupled to the second end of the transmitting device. The tip assembly further including a mirror and an image receiving aperture disposed adjacent to the mirror, the image receiving aperture and the mirror configured to receive and transmit an image the soldered connections to the camera through the image transmitting device, and at least one illumination device, the illumination device comprising a light source, a device for transmitting light from the light source to a light transmitting aperture disposed within the tip assembly, the light transmitting aperture disposed adjacent to the image receiving aperture.
In accordance with the present invention there is provided a method of inspecting soldered connections between an IC and a circuit board, the method including the steps of disposing a circuit board having at least one IC soldered thereto on a work surface of an inspection device. Aligning a tip of the inspection device with a row of soldered connections to be inspected. Using an optical inspection device to view the soldered connections between the IC and the circuit board, the optical inspection device including a camera, an image transmitting device comprising a generally cylindrical member having a first and second end the first end coupled to said camera, and a removable tip assembly coupled to the second end of the image transmitting device, the removable tip assembly including a main body housing at least one light transmitting aperture and a reflective device and an image receiving aperture disposed adjacent to the light transmitting aperture, the light transmitting aperture and image receiving aperture directed toward the soldered connections to be inspected, the reflective device adapted to receive and transmit and image of the soldered connections to the camera. Illuminating the soldered connections to be inspected, and visually examining the soldered connections between the IC and the circuit board by pivoting the camera, image transmitting device, and tip assembly about an optical centerline of the reflective device to view the upper or lower solder connections and rotating the camera, image transmitting device, and the tip assembly through about 90 degrees to view the sides of the soldered connections. Moving the IC relative to the tip assembly to visually inspect other soldered connections between the IC and the circuit board, and visually inspecting the gaps formed between the soldered connections for optical clarity.